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henrq lops
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Join Date: Mar 2009
Posts: 6

How Can I Measure the Centrifugal Force in an Electric Motor Rotor?

05/19/2011 4:58 PM

Hello dear colleagues,

I would like to consult you in order to solve a project question. We are redesigning a electric motor and we are changing the current rotor stack of sheet for another material which has a very lower tensile strength as well as the tensile rupture strength.

Then something came to my mind when I considered the "centrifugal" effect on the rotor teeth. Will the rotor endure the work?

I have the following data of the rotor:

-Mass: 180g

-RPM: 5500

-rotor radius: 21mm

-Fcf=???

Could you help me to solve this question?

Thanks and regards,
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Pathfinder Tags: centriful forces electric motor mechanical strength
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Anonymous Poster #1
#1

Re: How can I measure the centrifugal force in a electric motor rotor

05/19/2011 5:48 PM

Trying to use ferritic core? If yes your problem won't be destruction due to centrifugal forces but brittleness of material in acc-deceleration shocks. And no core loss benefits at frequences giving 5500 RPM S.M.
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Tornado
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#2

Re: How Can I Measure the Centrifugal Force in an Electric Motor Rotor?

05/19/2011 10:58 PM

F = ma; acentripetal = v2/r.

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Rixter
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#3

Re: How Can I Measure the Centrifugal Force in an Electric Motor Rotor?

05/20/2011 5:42 AM

Force = mass x 4∏2 x (RPM/60)2 x r

if you express mass in kg and r in meters, Force will be in Newtons

1 Newton = 0.22481 lb
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RHABE
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#4

Re: How Can I Measure the Centrifugal Force in an Electric Motor Rotor?

05/20/2011 11:03 AM

There is no simple answer to this question!

a. punched and stacked transformer steel (Fe + 4 to 8% Si) as rotor or ferrite or else?

b. which shape, to calculate where is highest stress: very often at the inner bore as this is where the stress is maximum in a non-teethed rotor. And this inner bore stress is often amplified by a press-fit shaft.

c. which shape of teeth? Very long ones to accommodate a lot of copper may have problems.

d. copper windings? or magnets?, how much weight to add?

We did run a 22mm rotor for an asynchronous motor made from high strength steel with copper-beryllium squirrel-cage windings and laser-welded end-rings up to 200,000rpm. Design speed was 300,000rpm. Bearings failed - not enough care taken about ball-bearing design of housing and shaft and more.

RHABE
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henrq lops
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Join Date: Mar 2009
Posts: 6
#5
In reply to #4

Re: How Can I Measure the Centrifugal Force in an Electric Motor Rotor?

05/23/2011 11:20 AM

Hello Rhabe,

you are right, we considered the stresses by the press fitted shaft. Using FEA we got a very good reference and idea of this kind of stress involved.

Our motor will have a small teeth ratio compared to present one.

Hopefully our prototype will survive the first test, based on those calculations.

Thanks and best regards,

Henrique
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